She is 90. I'm stressed about things she tells ppl on the phone. Example...
Today she told a family member she is always alone and hasn't seen anyone all day. She went with my parents to church this morning and saw many friends. I was cooking a special meal she likes in the kitchen and overheard her complaining. Yesterday our whole family went out to dinner together. Day before, we took her, my mom and daughter to lunch and shopping. She goes to my mom's to visit twice a week. I don't know what she expects.
What sort of "legalities" are you stressing out about with regard to moving grandma in with you? If it were me, I'd be worrying about losing my privacy, my mind, my autonomy, etc.....with legalities being at the very end of the list. There are a ton of things to consider before doing such a thing, ESPECIALLY if you think dementia is a factor! That's a real game changer, even for people who have lots of patience and experience dealing with dementia behaviors!
The only way to know if someone has dementia is to get them evaluated by a neurologist, psychiatrist or neuropsychologist.
Per your profile, gma is getting a pacemaker tomorrow and moving in with you and your family.
Have you all considered this move carefully? Who will be doing the caregiving?